The present invention relates to a structure of a bottom bracket for bicycles wherein the shaft of the bottom bracket is hollow and has grooves for receiving balls therein.
A conventional bicycle bottom bracket 70 is shown in FIG. 5 and generally includes a tube 80 with a shaft 71 rotatably received therein and two bearings 73 are respectively mounted to the shaft 71 to allow the shaft 71 be rotatable. An inner tube 72 is mounted to the shaft 71 and engaged between the two bearings 73 to position the bearings 73. Two threaded races 74 are respectively engaged with two threaded portions defined in an inner periphery of the tube 80. Therefore, the two bearings 73 are firmly positioned between the inner tube 72 and the two races 74. The shaft 71 is made of solid metal so that the whole weight is heavy and not satisfied by the requirements of modern bicycles. Besides, each bearing 73 received in the tube 80 has an outer casing which has a certain thickness so that the shaft 71 has to be designed to have two shrink ends so that the bearings 73 can be received in the tube 80. On the contrary, if the shaft 71 is made to be hollow to obtain a light in weight, the shrink ends 71 are adverse to bear large loads.
The present invention intends to provide a structure of bottom bracket wherein the shaft is hollowed and has grooves for receiving balls so that conventional outer casing of bearings can be improved and the diameter of the two ends of the shaft can be enlarged.
In accordance with one aspect of the present invention, there is provided a bottom bracket for bicycles and comprising a tube with a hollow shaft received therein and two first grooves defined in an outer periphery of the hollow shaft. Two collars are mounted to the hollow shaft and each have a second groove defined in an inner periphery thereof so that balls are engaged with the first grooves and the second grooves. An inner tube is mounted to the hollow shaft and engaged between two respective first ends of the two collars. Two races are respectively engaged with two ends of the tube and each race has a positioning flange extending radially inward from an inner periphery thereof so that the two positioning flanges are engaged with two respective second ends of the collars.
The primary object of the present invention is to provide a bottom bracket that has a hollow shaft which as a larger diameter so that the total weight of the bottom bracket is reduced and the strength of the hollow shaft is enforced as the diameter thereof is increased.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.